The present invention relates to virtual reality systems and methods. More particularly, the present invention provides a novel light emitting surface for providing a virtual image behind a surface. The virtual image can be viewed by an observer at large viewing angles for providing a relatively clear and realistic image. A variety of techniques have been used or proposed for viewing an image in a display system. Display systems can either be real image display systems or virtual image display systems. A typical real image display system generally includes a display surface, where an image is formed, and a control source, which creates an image including animated or still images onto the display. A human user often views the image on the display surface.
Known examples of real image display systems are movie theaters and cathode ray tubes, CRT. In a movie theater, the display surface is the screen where the image is projected and the control source is the film and the projector. In a CRT, the display surface is the phosphor coated faceplate of the CRT and the control source is the electron gun and associated electronics. A typical virtual image display system generally includes an optical system where the image is viewed and a control source, which creates images including animated or still images for the optical system. A human user observes the image though the optical system. Known examples of virtual image display systems include the image in a mirror and the image in a magnifying lens. In a mirror, the optical system is the mirror itself, and the control source is the real objects observed by the reflection in the mirror. In a magnifying lens, the optical system is the magnifying lens and the control source is the real objects under the magnifying lens. For the magnifying lens, the image is only in focus as perceived by the human observer when the distance between the lens and the control source is less than the focal length of the magnifying lens.
In more complex applications, techniques have been proposed to provide a panoramic view of a real image or in some cases a panoramic virtual image. A panoramic view is an image either real or virtual with a large field of view such that the observer sees the image fill a large portion of the view of the human vision system, the eyes. The human vision system has a well known field of view or visual field. Typically, a human can see with a horizontal field of view of 200 degrees and a vertical field of view of 135 degrees. (Foundations of Vision, Brian A. Wandell, Sinauer Associates Inc. Sunderland, Mass. 1995)
A known example of a panoramic display system is a planetarium. In a planetarium, the display surface is the dome of the planetarium, and the control source is a projection system which projects light from the control source to the dome of the planetarium. The observer views the projected image on the dome of the planetarium. The image is panoramic covering a very wide field of view, typically half of the total available field of view for the observers. Planetariums and similar panoramic display systems suffer from some problems. First, only observers standing near the center of the planetarium generally see an undistorted image. Observers standing near the edge of the planetarium begin to see the effects of the curvature of the dome surface on the image. Second, light from one region of the image projected onto the dome can scatter onto another region of the dome and then scatter into the observers eye, which causes a reduction in the perceived image quality. This reduction of image quality is commonly referred to as a reduction in the contrast ratio of an image. Third, to create the perception that the image is far away, the planetarium should be large. Typically planetariums are many tens of feet in diameter, and usually specifically constructed buildings are used for planetariums. Fourth, due to the large physical size of the planetariums, large amounts of light are required to illuminate the image on the surface of the dome of the planetarium.
Virtual panoramic display systems are also known. Many virtual display systems have several advantages over real display systems. First, most virtual display systems can provide a collimated image, i.e., the virtual image is apparently very far away, thus the virtual display system is generally more compact than a real display system. Second, a virtual display system in general requires less light because the virtual display system is more compact than a real display. Third, since the path of the light is controlled by the optical system, multiple scattering effects which can reduce the contrast ratio can be reduced or eliminated. Many virtual display systems have a disadvantage over a real display systems. One disadvantage is optical aberrations, i.e. distortions in the image introduced by the optical system. Optical aberrations can both limit the field of view of the optical system and limit the position of the observer relative to the optical system. One technique for reducing the aberrations of an optical system is to use the Schmidt principle in the design of the optical system. The Schmidt principle states that image formed by spherical concave reflector with an aperture at the center of curvature and using collimated input light, is a concentric spherical surface with half the radius of the spherical concave reflector.
An example of a virtual panoramic display is a "bird bath" magnifier system. A bird bath magnifier system uses a real image that provides illumination for the virtual image behind a concave mirror by way of a beam splitter. A bird bath magnifying system typically takes advantage of the Schmidt principle by using a curved real image, positioning the observer at the center of curvature of the mirror, and tilting beam splitter so that the curved real image, mirror and observer form an on axis optical system. A variety of limitations exist, however, using the bird bath magnifier system. For example, it generally has a limited field of view for the observer. The field of view is often limited to a horizontal field of view of less than about 40 degrees and a vertical field of view of less than about 30 degrees. Furthermore, the bird bath magnifier is often difficult to scale up to larger fields of view due to the complexity of using many real images and tiled beam splitters and properly overlapping the virtual images. Another limitation is the use of beam splitting elements which reduces the over all light efficiency of the magnifier. Accordingly, the bird bath magnifier is often extremely complex and expensive, has limited use, and has not been generally been used for commercial applications.
Another example of a virtual panoramic display system is commonly termed the "mirage" system. Similar to the bird bath magnifier, the mirage system includes an optical system, which has a large concave mirror. An image source is generally a projector, which uses specialized projection optics, to direct and illuminate an image onto a real display surface. The user sees a magnified image of the display surface in a large concave mirror. In most cases, the observer is below the display surface and sees the image of the display surface reflected in the mirror. This arrangement of display surface, concave mirror, and observer form an off axis optical system. The mirage system is more light efficient than the previous example since a beam splitter is not used in this optical arrangement. The mirage system, however, also has numerous limitations. The first limitation is the complexity introduced in the optical system by the off axis optical arrangement. The mirage system cannot take advantage of the Schmidt principle. The mirror used in the mirage system typically is a more complex shape than a simple spherical mirror. For example, it has a limited field of view, similar to the previous conventional system. In fact, the field of view is often less than about 200.degree. in the horizontal direction and less than about 45.degree. in the vertical direction. Again the off axis viewing limits the vertical field of view. It also creates significant optical aberrations (e.g., distortions) near edges of the image being displayed due to the off axis viewing of the virtual image. Furthermore, the mirage system is costly, and has limited use in the commercial world.
From the above, it is seen that a technique for viewing an image in a display system which is cost effective and provides clear images is desirable. Furthermore, a technique for viewing a panoramic virtual image without significant optical aberrations with both large horizontal and vertical fields of view is desirable. Furthermore a technique for viewing a panoramic virtual image where the quality of the image is insensitive to the position of the observer relative to the optical system is desirable.